During the past few decades, there has been an increasing interest in semiconductor devices, such as power metal oxide semiconductor field effective transistors (MOSFETs) used in various applications. The power MOSFET may usually have a polysilicon layer. The polysilicon layer can be used, for example, as a gate electrode or gate runner of the power MOSFET.
The power MOSFET may have two structures, e.g., a vertical diffused MOSFET (VDMOS) and a trench MOSFET in different applications. The VDMOS became available in mid-1970 due to the availability of planar technology. By late 1980, the trench MOSFET started to penetrate power MOSFET markets utilizing DRAM trench technology, which has improved Specific On Resistance (RDSON). However, the blockage voltage or breakdown voltage of trench MOSFET may be limited to low voltage (<600 V) due to more curvatures and stress of trench MOSFET structures. Also, the electrical field density tends to be higher in trench MOSFET due to positive curvature diode doping profiles, which may reduce the breakdown voltage. Besides breakdown issues, the threshold voltage and RDSON may be limited and cannot be easily further improved with the updated new and scale down semiconductor technologies.